<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="https://static.web.sdo.com/chuanshi/libs/common.css">
    <style>
        ul {
            display: flex;
            border: 2px solid red;
            width: 280px;
            flex-wrap: wrap;
        }

        li {
            width: 100px;
            height: 100px;
            color: #fff;
            font-size: 2em;
            box-sizing: border-box;
            padding: 5px;
            background-clip: content-box;
            background-color: brown;
        }
    </style>
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
</body>
</html>